github: return output if JSON parsing is not desired

[dawidd6]

There are endpoints that do not return a JSON object, like for example:
https://developer.github.com/v3/actions/workflow_runs/#list-workflow-run-logs

Add an option to not parse the response data as JSON.

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• Have you successfully run brew tests with your changes locally?

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[MikeMcQuaid]

Even simpler version suggested

[MikeMcQuaid]

Suggested change

	parse_json ? json : output
	parse_json output

[dawidd6]

You meant output only right?

[MikeMcQuaid]

Looks great, thanks @dawidd6!